Cal. Health & Safety Code § 39609

On or before December 31, 1989, and at least every three years thereafter, the state board shall complete a study on the feasibility of employing air quality models and other analytical techniques to distinguish between emission control measures on the basis of their relative ambient air quality impact. As part of this study, the state board shall determine whether adequate modeling capability exists to support the use of air quality indicators or alternative measures of progress as specified in subdivision (f) of Section 39607 and Section 40914. The state board shall consult with districts and affected groups in conducting this study, and, after a public hearing, shall prepare and transmit its findings to each district for its use in developing plans pursuant to Chapter 10 (commencing with Section 40910).